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Description/Abstract

Previous studies have shown chironomidsto be excellent indicators of environmental changeand training sets have been developed in order toallow these changes to be reconstructed quantitativelyfrom subfossil sequences. Here we present the resultsof an investigation into the relationships betweensurface sediment subfossil chironomid distributionand lake environmental variables from 42 lakes on theTibetan Plateau. Canonical correspondence analysis(CCA) revealed that of the 11measured environmentalvariables, salinity (measured as total dissolvedsolids TDS) was most important, accounting for 10.5% of the variance in the chironomid data. Thisvariable was significant enough to allow the developmentof quantitative inference models. A range ofTDS inference models were developed usingWeighted Averaging (WA), Partial Least Squares(PLS), Weighted Averaging–Partial Least Squares(WA–PLS), Maximum Likelihood (ML), ModernAnalogues Technique (MAT) and Modern AnaloguesTechniques weighted by similarity (WMAT).Evaluation of the site data indicated that four lakeswere major outliers, and after omitting these fromthetraining set the models produced jack-knifed coefficientsof determination (r2) between 0.60 and 0.80, androot-mean-squared errors of prediction (RMSEP)between 0.29 and 0.44 log10 TDS. The best performingmodel was the two-component WA–PLS model withr2jack = 0.80 and RMSEPjack = 0.29 log10 TDS. Themodel results were similar to other chironomidsalinitymodels developed in different regions, andthey also showed similar ecological groupings alongthe salinity gradientwith respect to freshwater/salinitythresholds and community diversity. These resultstherefore indicate that similar processes may becontrolling chironomid distribution across salinitygradients irrespective of biogeographical constraints.The performance of the transfer functions illustratesthat chironomid assemblages from the Tibetan Plateaulakes are clearly sensitive indicators of salinity.The models will therefore allow the quantification oflong-term records of past water salinity for lacustrinesites across the Tibetan Plateau, which has important implications for future hydrological research in theregion.